Born Helena Kowalska in the small Polish town of Lodz, St. Faustina was one of 10 children in a family struggling to survive during World War I. Because her parents needed her to help support the family, she received only three years of education. At age 20, she answered Christ's call and entered the Congregation of the Sisters of Our Lady of Mercy. While at the convent, the Lord spoke to her and told her that she was to be an apostle of his mercy. Despite her lack of schooling, she wrote several notebooks under the guidance of Christ that contained profound theological insights. Many of these writings spoke of God's limitless mercy.

Though she had many sufferings during her life, St. Faustina maintained and spread the joy of God's mercy. Despite contracting what was likely tuberculosis, St. Faustina persisted in prayer and the sacraments. She died in 1938, and was canonized by St. John Paul II in 2000, making her the first saint of the new millennium. St. John Paul II also helped to spread St. Faustina's message of Divine Mercy, instituting Divine Mercy Sunday on the second Sunday of Easter and promoting the Divine Mercy Chaplet. Today, millions of Catholics are inspired by St. Faustina's writings, which are compiled into a single diary entitled Divine Mercy in My Soul.